Since the 1950s, scientists have developed neutron scattering techniques to better utilize neutrons in research areas such as nuclear physics, advanced synthetic materials development, and macroscopic structural analysis. Research facilities such as the Spallation Neutron Source are dedicated to neutron-related science. Such facilities require complex generation, focus, and collection of neutrons. In the interest of time and cost effectiveness, it is essential to develop superior methods to capture and focus neutrons.
Neutrons are typically delivered close to a sample by the use of a neutron guide made of supermirrors to direct the source beam of neutrons. The neutron guide moves the source phase space close to the sample to increase the flux on samples. If the sample is small and the guide tube not in direct contact with the sample, however, the divergence of the beam after the guide must be limited to maintain a small beam on the sample. This makes it highly advantageous to use focusing for small samples, and in realistic conditions, it is estimated that a simple Kirkpatrick-Baez (KB) super mirror system can focus about 100 times as many neutrons onto a 100 micron sized spot at the sample than is possible with a guide tube. Much better performance than even this major improvement over common practice will be possible if the convergence angles of the neutrons from the KB mirror system can be increased.
A single mirror surface focusing in the meridional direction can collect at most a convergence 2 times its critical angle, and a practical single mirror surface can collect only about its critical angle in convergence. A sagittal focusing or figure of revolution mirror system (e.g., a Wolter Optics system) can collect up to 4 times its critical angle, but there is a hole in the convergence distribution, and it is difficult or impossible to produce a system of this type that can achieve the glancing angles needed to deflect thermal neutrons. Kumakov lenses can collect large divergences, but are very inefficient because they have intrinsically small scattering angles and large absorption in the optics.
U.S. Pat. Nos. 5,082,621 and 5,167,912, both to Wood, show a neutron reflecting supermirror structure, however, both are limited to the structure of the supermirror surface and do not address the geometry of how to use the supermirror surface for focusing. In addition, there is no discussion of an array composition of supermirrors nor nondispersive focusing of neutrons via an array composition of supermirrors.
U.S. Pat. No. 5,949,840 to Greene teaches a neutron guide, however, the guide as disclosed is limited to fabrication of the guide surface and structure, and does not address the geometry of how to use the guide for focusing neutrons. In addition, there is no discussion of an array composition of supermirrors nor nondispersive focusing of neutrons via an array composition of supermirrors.
Accordingly, a need in the art exists for a method to extend the KB mirror focusing geometry to allow nondispersive focusing of neutrons with a convergence on a sample much larger than is possible with existing KB optical schemes.